BRYOZOA. 667 



STREBLOTRYPA RADIALIS Ulrich. 



PI. LXXH, fig. 2-2d. 



Zoarium consisting of slender, dichotomouslj dividing stems 

 about 1 mrn. in diameter, the whole forming a bushy mass 

 growing from a central point out in all directions. Zooecia aper- 

 tures small, suboval, slightly truncated posteriorly, about 0.1 

 mm, long, two-thirds as wide, occupying the anterior half of 

 the bottom of a sloping area. Area hexagonal in outline, trun- 

 cated at the ends, about 0.28 mm. long, by 0.14 mm. wide, 

 sloping gradually down into the aperture, which, as has been 

 said, occupies the anterior half of the bottom. The posterior 

 slope is more gentle than the anterior, and presents the mouths 

 of from two to four very minute pores, which, unless the speci- 

 mens are exceptionally preserved, are liable to be overlooked. 

 The areas are ranged in very regular longitudinal and diago- 

 nally intersecting series, with eleven or twelve in 3 mm. longi- 

 tudinally, and six in 1 mm. diagonally. The summit of the 

 zigzag ridges formed by them is rather sharply defined and 

 carries a crowded series of very minute granules. 



The internal characters are very well shown by the illustra- 

 tions. The chief distinctive feature shown by thin sections is 

 the radial arrangement observed in transverse sections. 



This species presents much superficial resemblance to Rhombo- 

 pora attenuata, but a close comparison shows that they differ 

 in important particulars. Of these the presence of small pores 

 back of the zooecia apertures in the present species, is the prin- 

 cipal one. The apertures are also smaller and not situated in 

 the middle of the area. S. subspinosa, of the Chester limestone, 

 differs slightly in its measurements, has the areas less sharply 

 defined, and the ridges somewhat tuberculated. 



Position and locality: Keokuk group, near Xauvoo, 111., and 

 Bentonsport. Iowa. 



STREBLOTRYPA NICKLESI Ulrich. 



PL LXXI. fles. 9-9c. 



Zoarium consisting of slender, sub-cylindrical, bifurcating 

 stems, about 0.5 mm. in diameter. Zooecial tubes very long. 



